Method of implanting a subcutaneous defibrillator

ABSTRACT

A subcutaneous implantable cardioverter-defibrillator is disclosed which has an electrically active canister which houses a source of electrical energy, a capacitor, and operational circuitry that senses the presence of potentially fatal heart rhythms. At least one subcutaneous electrode that serves as the opposite electrode from the canister is attached to the canister via a lead system. Cardioversion-defibrillation energy is delivered when the operational circuitry senses a potentially fatal heart rhythm. There are no transvenous, intracardic, or epicardial electrodes. A method of subcutaneously implanting the cardioverter-defibrillator is also disclosed as well as a kit for conducting the method.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/529,671, filed Sep. 28, 2006 now U.S. Pat. No. 7,720,534; which is acontinuation of U.S. patent application Ser. No. 11/447,711, filed Jun.6, 2006 and now U.S. Pat. No. 7,657,311; which is a continuation of U.S.patent application Ser. No. 10/790,903, filed Mar. 1, 2004 and now U.S.Pat. No. 7,076,294; which is a continuation of U.S. patent applicationSer. No. 09/663,607, filed Sep. 18, 2000 and now U.S. Pat. No.6,721,597; the entire disclosures of which are all incorporated hereinby reference.

This application is related to U.S. patent application Ser. No.09/663,606, filed Sep. 18, 2000, now U.S. Pat. No. 6,647,292 and titledUNITARY SUBCUTANEOUS ONLY IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR ANDOPTIONAL PACER, the entire disclosure of which is herein incorporated byreference.

FIELD

The present invention relates to an apparatus and method for performingelectrical cardioversion/defibrillation and optional pacing of the heartvia a totally subcutaneous non-transvenous system.

BACKGROUND

Defibrillation/cardioversion is a technique employed to counterarrhythmic heart conditions including some tachycardias in the atriaand/or ventricles. Typically, electrodes are employed to stimulate theheart with electrical impulses or shocks of a magnitude substantiallygreater than pulses used in cardiac pacing.

Defibrillation/cardioversion systems include body implantable electrodesand are referred to as implantable cardioverter/defibrillators (ICDs).Such electrodes can be in the form of patches applied directly toepicardial tissue, or at the distal and regions of intravascularcatheters, inserted into a selected cardiac chamber. U.S. Pat. Nos.4,603,705; 4,693,253; 4,944,300; and 5,105,810, the disclosures of whichare all incorporated herein by reference, disclose intravascular ortransvenous electrodes, employed either alone or in combination with anepicardial patch electrode. Compliant epicardial defibrillatorelectrodes are disclosed in U.S. Pat. Nos. 4,567,900 and 5,618,287, thedisclosures of which are incorporated herein by reference. A sensingepicardial electrode configuration is disclosed in U.S. Pat. No.5,467,503, the disclosure of which is incorporated herein by reference.

In addition to epicardial and transvenous electrodes, subcutaneouselectrode systems have also been developed. For example, U.S. Pat. Nos.5,342,407 and 5,603,732, the disclosures of which are incorporatedherein by reference, teach the use of the pulse monitor/generatorsurgically implanted into the abdomen and subcutaneous electrodesimplanted in the thorax. This system is far more complicated to use thancurrent ICD systems using transvenous lead systems together with anactive can electrode, and therefore, it has no practical use. It has, infact, never been used because of the surgical difficulty of applyingsuch a device (3 incisions), the impractical abdominal location of thegenerator and the electrically poor defibrillation aspects of such asystem.

Recent efforts to improve the efficiency of ICDs have led manufacturersto produce ICDs which are small enough to be implanted in the pectoralregion. In addition, advances in circuit design have enabled the housingof the ICD to form a subcutaneous electrode. Some examples of ICDs inwhich the housing of the ICD serves as an optional additional electrodeare described in U.S. Pat. Nos. 5,133,353; 5,261,400; 5,620,477; and5,658,321, the disclosures of which are incorporated herein byreference.

ICDs are now an established therapy for the management of lifethreatening cardiac rhythm disorders, primarily ventricular fibrillation(V-Fib). ICDs are very effective at treating V-Fib, but are therapiesthat are still require significant surgery.

As ICD therapy becomes more prophylactic in nature and used inprogressively less ill individuals, especially children at risk ofcardiac arrest, the requirement of ICD therapy to use intravenouscatheters and transvenous leads in an impediment to very long termmanagement as most individuals will begin to develop complicationsrelated to lead system malfunction sometime in the 5- to 10-year timeframe, often earlier. In addition, chronic transvenous lead systems,their reimplantation and removals, can damage major cardiovascularvenous systems and the tricuspid valve, as well as result in lifethreatening perforations of the great vessels and heart. Consequently,use of transvenous lead systems, despite their many advantages, is notwithout their chronic patient management limitations in those with lifeexpectancies of greater than 5 years. The problem of lead complicationsis even greater in children where body growth can substantially altertransvenous lead function and lead to additional cardiovascular problemsand revisions. Moreover, transvenous ICD systems also increase cost andrequire specialized interventional rooms and equipment as well asspecial skill for insertion. These systems are typically implanted bycardiac electrophysiologists who have had a great deal of extratraining.

In addition to the background related to ICD therapy, the presentinvention requires a brief understanding of automatic externaldefibrillator (AED) therapy. AEDs employ the use of cutaneous patchelectrodes to effect defibrillation under the direction of bystanderuser who treats the patient suffering from V-Fib. AEDs can be aseffective as an ICD if applied to the victim promptly within 2 to 3minutes.

AED therapy has great appeal as a tool for diminishing the risk of deathin public venues such as in air flight. However, an AED must be used byanother individual, not the person suffering from the potentially fatalrhythm. It is more of a public health tool than a patient-specific toollike an ICD. Because greater than 75% of cardiac arrests occur in thehome, and over half occur in the bedroom, patients at risk of cardiacarrest are often alone or asleep and cannot be helped in time with anAED. Moreover, its success depends to a reasonable degree on anacceptable level of skill and calm by the bystander user.

What is needed therefore, especially for children and for prophylacticlong term use, is a combination of the two forms of therapy which wouldprovide prompt and near-certain defibrillation, like an ICD, but withoutthe long-term adverse sequelae of a transvenous lead system whilesimultaneously using most of the simpler and lower cost technology of anAED. We call such a device a subcutaneous only ICD (S-ICD) and isdescribed in detail below.

SUMMARY

The preferred embodiment for the subcutaneous only ICD (S-ICD) withoptional pacing consists of five basic components: 1) an electricallyactive canister housing a battery supply, capacitor and operationalcircuitry wherein the housing serves as an electrode and replaces oneconventional lead of the prior art systems; 2) one or more subcutaneouscombined high voltage/sense/pace electrodes emanating from the S-ICDhousing; 3) sense circuitry suitable to an ICD or AED V-FIB detectionalgorithm; 4) an application system for simple insertion of thesubcutaneous lead; and 5) a cutaneous test system designed to estimatethe best location of the S-ICD for each patient. Therefore, notransvenous lead system is necessary, eliminating a significantimpediment to broader scale prophylactic use and especially use inchildren.

The active canister housing will provide energy and voltage intermediateto that available with ICD and AEDs. The typical maximum voltagenecessary for ICDs using most biphasic waveforms is approximately 750 Vand associated maximum energy of approximately 40 J. The typical maximumvoltage necessary for AEDs is approximately 2000-5000 V with anassociated maximum energy of approximately 150-360 J. The S-ICD of thepresent invention will use voltages in the range of 800 to 2000 V andassociated with energies of approximately 40-150 J. The canister couldbe employed as either a cathode or an anode.

In the preferred embodiment, only one subcutaneous high voltageelectrode, of opposite polarity to the canister, will be used but nolimit is placed on the number of subcutaneous electrodes that may berequired to achieve optimal S-ICD function. The subcutaneous electrode,composed of silicone or polyurethane insulation, will have a minimum of1 electrode but, in the preferred embodiment, will have 3: a highvoltage, low-impedance coil electrode approximately 5-10 cm in lengthand two low voltage, high impedance sense electrodes at the tip. Thespacing of the sense electrodes will be approximately 4 cm to provide areasonable QRS signal from a subcutaneous extracardic sampling locationbut may be of variable length to allow for sense optimization. In thepreferred embodiment, the sense electrodes are placed proximal to thehigh voltage lead, contrary to typical transvenous ICD lead systems, butalternative locations are allowed.

The sense circuitry in the preferred embodiment is designed to be highlysensitive and specific to the presence or absence of life threateningventricular arrhythmias only. Features of the detection algorithm areprogrammable, but the algorithm is focused on the detection of V-Fib andhigh rate ventricular tachycardia (V-Tach) of greater than 240 bpm. Thistype of cardioverter-defibrillator is not necessarily designed toreplace ICD therapy for those with pre-identified problems ofV-Tach/V-Fib or even atrial fibrillation, but is particularly geared touse as a prophylactic, long-term device, used for the life of thepatient at risk of his/her first V-Fib/V-Tach event. The device of thepresent invention may infrequently be used for an actuallife-threatening event but can be employed in large populations ofindividuals at modest risk and with modest cost by physicians of limitedexperience. Consequently, the preferred embodiment of the presentinvention focuses only on the detection and therapy of the mostmalignant rhythm disorders. As part of the detection algorithm'sapplicability to children, the upper rate range is programmable upwardfor use in children, who are known to have more rapid supraventriculartachycardias as well as more rapid ventricular tachycardias compared toadults.

The incision to apply the device of the present invention can beanywhere on the thorax although in the preferred embodiment, the deviceof the present invention will be applied in the left anteriormid-clavicular line approximately at the level of the mammary creasebeneath the left areolus. The S-ICD can be placed subcutaneously as anyICD is currently placed. One critical difference is the highvoltage/sense lead is placed totally subcutaneously with a speciallydesigned curved introducer set, through which local anesthetic can bedelivered, if necessary, followed by insertion of the lead system viathe same incision used for generator insertion. The lead, however,unlike the generator, is directed laterally and posterior forpositioning of the lead in the posterior thoracic region, ideally in theleft posterior axillary line at the level of the inferior scapula tip.Such a lead position will allow for a good transthoracic currentdelivery vector as well as positioning of the proximally positionedsense bipole in a good location for identification of the QRS. There isno transvenous component.

The final component of the S-ICD is a cutaneous test electrode systemdesigned to simulate the subcutaneous high voltage shock electrodesystem as well as the QRS cardiac rhythm detection system. This testelectrode system is comprised of a cutaneous patch electrode of similarsurface area and impedance to that of the S-ICD canister itself togetherwith a cutaneous strip electrode comprising a defibrillation strip aswell as two button electrodes for sensing of the QRS. Several cutaneousstrip electrodes are available to allow for testing various bipolespacing to optimize signal detection in order to allow for variablesense bipole spacings on leads of different length and electrode spacingand configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is now made tothe drawings where like numerals represent similar objects throughoutthe figures where:

FIG. 1 is a schematic view of a Subcutaneous ICD (S-ICD) of the presentinvention;

FIG. 2 is a schematic view of an alternate embodiment of a subcutaneouselectrode of the present invention;

FIG. 3 is a schematic view of an alternate embodiment of a subcutaneouselectrode of the present invention;

FIG. 4 is a schematic view of the S-ICD and lead of FIG. 1subcutaneously implanted in the thorax of a patient;

FIG. 5 is a schematic view of the S-ICD and lead of FIG. 2subcutaneously implanted in an alternate location within the thorax of apatient;

FIG. 6 is a schematic view of the S-ICD and lead of FIG. 3subcutaneously implanted in the thorax of a patient;

FIG. 7 is a schematic view of the method of making a subcutaneous pathfrom the preferred incision and housing implantation point to atermination point for locating a subcutaneous electrode of the presentinvention;

FIG. 8 is a schematic view of an introducer set for performing themethod of lead insertion of any of the described embodiments;

FIG. 9 is a schematic view of an alternative S-ICD of the presentinvention illustrating a lead subcutaneously and serpiginously implantedin the thorax of a patient for use particularly in children;

FIG. 10 is a schematic view of an alternate embodiment of an S-ICD ofthe present invention;

FIG. 11 is a schematic view of the S-ICD of FIG. 10 subcutaneouslyimplanted in the thorax of a patient;

FIG. 12 is a schematic view of a yet a further embodiment where thecanister of the S-ICD of the present invention is shaped to beparticularly useful in placing subcutaneously adjacent and parallel to arib of a patient; and

FIG. 13 is a schematic of a different embodiment where the canister ofthe S-ICD of the present invention is shaped to be particularly usefulin placing subcutaneously adjacent and parallel to a rib of a patient.

DETAILED DESCRIPTION

Turning now to FIG. 1, the S-ICD of the present invention isillustrated. The S-ICD consists of an electrically active canister 11and a subcutaneous electrode 13 attached to the canister. The canisterhas an electrically active surface 15 that is electrically insulatedfrom the electrode connector block 17 and the canister housing 16 viainsulating area 14. The canister can be similar to numerous electricallyactive canisters commercially available in that canister will contain abattery supply, capacitor and operational circuitry. Alternatively, thecanister can be thin and elongated to conform to the intercostals space.The circuitry will be able to monitor cardiac rhythms for tachycardiaand fibrillation, and if detected, will initiate charging the capacitorand then delivering cardioversion/defibrillation energy through theactive surface of the housing and to the subcutaneous electrode.Examples of such circuitry are described in U.S. Pat. Nos. 4,693,253 and5,105,810, the entire disclosures of which are herein incorporated byreference. The canister circuitry can providecardioversion/defibrillation energy in different types of waveforms. Inthe preferred embodiment, a 100 uF biphasic wave form is used ofapproximately 10-20 ms total duration and with the initial phasecontaining approximately ⅔ of the energy, however, any type of the waveform can be utilized such as monophasic, biphasic, multiphasic oralternative waveforms as is known in the art.

In addition to providing cardioversion/defibrillation energy, thecircuitry can also provide transthoracic cardiac pacing energy. Theoptional circuitry will be able to monitor the heart for bradycardiaand/or tachycardia rhythms. Once a bradycardia or tachycardia rhythm isdetected, the circuitry can then deliver appropriate pacing energy atappropriate intervals through the active surface and the subcutaneouselectrode. Pacing stimuli will be biphasic in the preferred embodimentand similar in pulse amplitude to that used for conventionaltransthoracic pacing.

The same circuitry can also be used to deliver low amplitude shocks onthe T-wave for induction of ventricular fibrillation for testing S-ICDperformance in treating V-Fib as is described in U.S. Pat. No.5,129,392, the entire disclosure of which is hereby incorporated byreference. Also, the circuitry can be provided with rapid induction ofventricular fibrillation or ventricular tachycardia using rapidventricular pacing. Another optional way for inducing ventricularfibrillation would be to provide a continuous low voltage, i.e., about 3volts, across the heart during the entire cardiac cycle.

Another optional aspect of the present invention is that the operationalcircuitry can detect the presence of atrial fibrillation as described inOlson, W. et al. “Onset And Stability For Ventricular TachyarrhythmiaDetection in an Implantable Cardioverter and Defibrillator, Computers inCardiology (1986) pp 167-170. Detection can be provided via R-R Cyclelength instability detection algorithms. Once atrial fibrillation hasbeen detected, the operational circuitry will then provide QRSsynchronized atrial defibrillation/cardioversion using the same shockenergy and waveshape characteristics used for ventriculardefibrillation/cardioversion.

The sensing circuitry will utilize the electronic signals generated fromthe heart and will primarily detect QRS waves. In one embodiment, thecircuitry will be programmed to detect only ventricular tachycardias orfibrillations. The detection circuitry will utilize in its most directform a rate detection algorithm that triggers charging of the capacitoronce the ventricular rate exceeds some predetermined level for a fixedperiod of time: for example, if the ventricular rate exceeds 240 bpm onaverage for more that 4 seconds. Once the capacitor is charged, aconfirmatory rhythm check would ensure that the rate persists for atleast another 1 second before discharge. Similarly, terminationalgorithms could be instituted that ensure that a rhythm less than 240bpm persisting for at least 4 seconds before the capacitor charge isdrained to an internal resistor. Detection, confirmation and terminationalgorithms as are described above and in the art can be modulated toincrease sensitivity and specificity by examining QRS beat-to-beatuniformity, QRS signal frequency content, R-R interval stability data,and signal amplitude characteristics all or part of which can be used toincrease or decrease both sensitivity and specificity of S-ICDarrhythmia detection function.

In addition to use of the sense circuitry for detection of V-Fib orV-Teach by examining the QRS waves, the sense circuitry can check forthe presence or the absence of respiration. The respiration rate can bedetected by monitoring the impedance across the thorax usingsubthreshold currents delivered across the active can and the highvoltage subcutaneous lead electrode and monitoring the frequency inundulation in the waveform that results from the undulations oftransthoracic impedance during the respiratory cycle. If there is noundulation, then the patient is not respiring and this lack ofrespiration can be used to confirm the QRS findings of cardiac arrest.The same technique can be used to provide information about therespiratory rate or estimate cardiac output as described in U.S. Pat.Nos. 6,095,987; 5,423,326; and 4,450,527, the entire disclosures ofwhich are incorporated herein by reference.

The canister of the present invention can be made out of titanium alloyor other presently preferred electrically active canister designs.However, it is contemplated that a malleable canister that can conformto the curvature of the patient's chest will be preferred. In this way,the patient can have a comfortable canister that conforms to the shapeof the patient's rib cage. Examples of conforming canisters are providedin U.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. Therefore, the canister can be made out ofnumerous materials such as medical grade plastics, metals, and alloys.In the preferred embodiment, the canister is smaller than 60 cc volumehaving a weight of less than 100 gms for long-term wearability,especially in children. The canister and the lead of the S-ICD can alsouse fractal or wrinkled surfaces to increase surface area to improvedefibrillation capability. Because of the primary prevention role of thetherapy and the likely need to reach energies over 40 Joules, a featureof the preferred embodiment is that the charge time for the therapy,intentionally be relatively long to allow capacitor charging within thelimitations of device size. Examples of small ICD housings are disclosedin U.S. Pat. Nos. 5,957,956 and 5,405,363, the entire disclosures ofwhich are herein incorporated by reference.

Different subcutaneous electrodes 13 of the present invention areillustrated in FIGS. 1-3. Turning to FIG. 1, the lead 21 for thesubcutaneous electrode is preferably composed of silicone orpolyurethane insulation. The electrode is connected to the canister atits proximal end via connection port 19 which is located on anelectrically insulated are 17 of the canister. The electrode illustratedis a composite electrode with three different electrodes attached to thelead. In the embodiment illustrated, an optional anchor segment 52 isattached at the most distal end of the subcutaneous electrode foranchoring the electrode into soft tissue such that the electrode doesnot dislodge after implantation.

The most distal electrode on the composite subcutaneous electrode is acoil electrode 27 that is used for delivering the high voltagecardioversion/defibrillation energy across the heart. The coilcardioversion/defibrillation electrode is about 5-10 cm in length.Proximal to the coil electrode are two sense electrodes, a first senseelectrode 25 is located proximally to the coil electrode and a secondsense electrode 23 is located proximally to the first sense electrode.The sense electrodes are spaced far enough apart to be able to have goodQRS detection. This spacing can range from 1 to 10 cm with 4 cm beingpresently preferred. The electrodes may or may not be circumferentialwith the preferred embodiment. Having the electrodes non-circumferentialand positioned outward, toward the skin surface, is a means to minimizemuscle artifact and enhance QRS signal quality. The sensing electrodesare electrically isolated from the cardioversion/defibrillationelectrode via insulating areas 29. Similar types ofcardioversion/defibrillation electrodes are currently commerciallyavailable in a transvenous configuration. For example, U.S. Pat. No.5,534,022, the entire disclosure of which is herein incorporated byreference, discloses a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement are contemplated within the scope ofthe invention. One such modification is illustrated in FIG. 2 where thetwo sensing electrodes 25 and 23 are non-circumferential sensingelectrodes and one is located at the distal end, the other is locatedproximal thereto with the coil electrode located in between the twosensing electrodes. In this embodiment, the sense electrodes are spacedabout 6 to about 12 cm apart depending on the length of the coilelectrode used. FIG. 3 illustrates yet a further embodiment where thetwo sensing electrodes are located at the distal end to the compositeelectrode with the coil electrode located proximally thereto. Otherpossibilities exist and are contemplated within the present invention.For example, having only one sensing electrode, either proximal ordistal to the coil cardioversion/defibrillation electrode with the coilserving as both a sensing electrode and a cardioversion/defibrillationelectrode.

It is also contemplated within the scope of the invention that thesensing of QRS waves (and transthoracic impedance) can be carried outvia sense electrodes on the canister housing or in combination with thecardioversion/defibrillation coil electrode and/or the subcutaneous leadsensing electrode(s). In this way, sensing could be performed via theone coil electrode located on the subcutaneous electrode and the activesurface on the canister housing. Another possibility would be to haveonly one sense electrode located on the subcutaneous electrode and thesensing would be performed by that one electrode and either the coilelectrode on the subcutaneous electrode or by the active surface of thecanister. The use of sensing electrodes on the canister would eliminatethe need for sensing electrodes on the subcutaneous electrode. It isalso contemplated that the subcutaneous electrode would be provided withat least one sense electrode, the canister with at least one senseelectrode, and if multiple sense electrodes are used on either thesubcutaneous electrode and/or the canister, that the best QRS wavedetection combination will be identified when the S-ICD is implanted andthis combination can be selected, activating the best sensingarrangement from all the existing sensing possibilities. Turning againto FIG. 2, two sensing electrodes 26 and 28 are located on theelectrically active surface 15 with electrical insulator rings 30 placedbetween the sense electrodes and the active surface. These canistersense electrodes could be switched off and electrically insulated duringand shortly after defibrillation/cardioversion shock delivery. Thecanister sense electrodes may also be placed on the electricallyinactive surface of the canister. In the embodiment of FIG. 2, there areactually four sensing electrodes, two on the subcutaneous lead and twoon the canister. In the preferred embodiment, the ability to changewhich electrodes are used for sensing would be a programmable feature ofthe S-ICD to adapt to changes in the patient physiology and size (in thecase of children) over time. The programming could be done via the useof physical switches on the canister, or as presently preferred, via theuse of a programming wand or via a wireless connection to program thecircuitry within the canister.

The canister could be employed as either a cathode or an anode of theS-ICD cardioversion/defibrillation system. If the canister were thecathode, then the subcutaneous coil electrode would be the anode.Likewise, if the canister were the anode, then the subcutaneouselectrode would be the cathode.

The active canister housing will provide energy and voltage intermediateto that available with ICDs and most AEDs. The typical maximum voltagenecessary for ICDs using most biphasic waveforms is approximately 750Volts with an associated maximum energy of approximately 40 Joules. Thetypical maximum voltage necessary for AEDs is approximately 2000-5000Volts with an associated maximum energy of approximately 200-360 Joulesdepending upon the model and waveform used. The S-ICD of the presentinvention uses maximum voltages in the range of about 800 to about 2000Volts and is associated with energies of about 40 to about 150 Joules.The capacitance of the S-ICD could range from about 50 to about 200microfarads.

The sense circuitry contained within the canister is highly sensitiveand specific for the presence or absence of life threatening ventriculararrhythmias. Features of the detection algorithm are programmable andthe algorithm is focused on the detection of V-FIB and high rate V-TACH(>240 bpm). Although the S-ICD of the present invention may rarely beused for an actual life-threatening event, the simplicity of design andimplementation allows it to be employed in large populations of patientsat modest risk with modest cost by non-cardiac electrophysiologists.Consequently, the S-ICD of the present invention focuses mostly on thedetection and therapy of the most malignant rhythm disorders. As part ofthe detection algorithm's applicability to children, the upper raterange is programmable upward for use in children, known to have rapidsupraventricular tachycardias and more rapid ventricular fibrillation.Energy levels also are programmable downward in order to allow treatmentof neonates and infants.

Turning now to FIG. 4, the optimal subcutaneous placement of the S-ICDof the present invention is illustrated. As would be evident to a personskilled in the art, the actual location of the S-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the Figures only for help in understandingwhere the canister and coil electrode are three-dimensionally located inthe thorax of the patient. The S-ICD canister with the active housing islocated in the left mid-clavicular line approximately at the level ofthe inframammary crease at approximately the 5th rib. The lead 21 of thesubcutaneous electrode traverses in a subcutaneous path around thethorax terminating with its distal electrode end at the posterioraxillary line, ideally just lateral to the left scapula. This way thecanister and subcutaneous cardioversion/defibrillation electrode providea reasonably good pathway for current delivery to the majority of theventricular myocardium.

FIG. 5 illustrates a different placement of the present invention. TheS-ICD canister with the active housing is located in the left posterioraxillary line approximately lateral to the tip of the inferior portionof the scapula. This location is especially useful in children. The lead21 of the subcutaneous electrode traverses in a subcutaneous path aroundthe thorax terminating with its distal electrode end at the anteriorprecordial region, ideally in the inframammary crease. FIG. 6illustrates the embodiment of FIG. 1 subcutaneously implanted in thethorax with the proximal sense electrodes 23 and 25 located atapproximately the left axillary line with thecardioversion/defibrillation electrode just lateral to the tip of theinferior portion of the scapula.

FIG. 7 schematically illustrates the method for implanting the S-ICD ofthe present invention. An incision 31 is made in the left anterioraxillary line approximately at the level of the cardiac apex. Thisincision location is distinct from that chosen for S-ICD placement andis selected specifically to allow both canister location more mediallyin the left inframammary crease and lead positioning more posteriorlyvia the introducer set (described below) around to the left posterioraxillary line lateral to the left scapula. That said, the incision canbe anywhere on the thorax deemed reasonable by the implanting physicianalthough in the preferred embodiment, the S-ICD of the present inventionwill be applied in this region. A subcutaneous pathway 33 is thencreated medially to the inframammary crease for the canister andposteriorly to the left posterior axillary line lateral to the leftscapula for the lead.

The S-ICD canister 11 is then placed subcutaneously at the location ofthe incision or medially at the subcutaneous region at the leftinframammary crease. The subcutaneous electrode 13 is placed with aspecially designed curved introducer set 40 (see FIG. 8). The introducerset comprises a curved trocar 42 and a stiff curved peel away sheath 44.The peel away sheath is curved to allow for placement around the ribcage of the patient in the subcutaneous space created by the trocar. Thesheath has to be stiff enough to allow for the placement of theelectrodes without the sheath collapsing or bending. Preferably thesheath is made out of biocompatible plastic material and is perforatedalong its axial length to allow for it to split apart into two sections.The trocar has a proximal handle 41 and a curved shaft 43. The distalend 45 of the trocar is tapered to allow for dissection of asubcutaneous path 33 in the patient. Preferably, the trocar iscannulated having a central lumen 46 and terminating in an opening 48 atthe distal end. Local anesthetic such as lidocaine can be delivered, ifnecessary, through the lumen or through a curved and elongated needledesigned to anesthetize the path to be used for trocar insertion shouldgeneral anesthesia not be employed. The curved peel away sheath 44 has aproximal pull tab 49 for breaking the sheath into two halves along itsaxial shaft 47. The sheath is placed over a guidewire inserted throughthe trocar after the subcutaneous path has been created. Thesubcutaneous pathway is then developed until it terminatessubcutaneously at a location that, if a straight line were drawn fromthe canister location to the path termination point the line wouldintersect a substantial portion of the left ventricular mass of thepatient. The guidewire is then removed leaving the peel away sheath. Thesubcutaneous lead system is then inserted through the sheath until it isin the proper location. Once the subcutaneous lead system is in theproper location, the sheath is split in half using the pull tab 49 andremoved. If more than one subcutaneous electrode is being used, a newcurved peel away sheath can be used for each subcutaneous electrode.

The S-ICD will have prophylactic use in adults where chronictransvenous/epicardial ICD lead systems pose excessive risk or havealready resulted in difficulty, such as sepsis or lead fractures. It isalso contemplated that a major use of the S-ICD system of the presentinvention will be for prophylactic use in children who are at risk forhaving fatal arrhythmias, where chronic transvenous lead systems posesignificant management problems. Additionally, with the use of standardtransvenous ICDs in children, problems develop during patient growth inthat the lead system does not accommodate the growth. FIG. 9 illustratesthe placement of the S-ICD subcutaneous lead system such that theproblem that growth presents to the lead system is overcome. The distalend of the subcutaneous electrode is placed in the same location asdescribed above providing a good location for the coilcardioversion/defibrillation electrode 27 and the sensing electrodes 23and 25. The insulated lead 21 however is no longer placed in a tautconfiguration. Instead, the lead is serpiginously placed with aspecially designed introducer trocar and sheath such that it hasnumerous waves or bends. As the child grows, the waves or bends willstraighten out, lengthening the lead system while maintaining properelectrode placement. Although it is expected that fibrous scarring,especially around the defibrillation coil, will help anchor it intoposition to maintain its posterior position during growth, a lead systemwith a distal tine or screw electrode anchoring system 52 can also beincorporated into the distal tip of the lead to facilitate leadstability (see FIG. 1). Other anchoring systems can also be used such ashooks, sutures, or the like.

FIGS. 10 and 11 illustrate another embodiment of the present S-ICDinvention. In this embodiment there are two subcutaneous electrodes 13and 13′ of opposite polarity to the canister. The additionalsubcutaneous electrode 13′ is essentially identical to the previouslydescribed electrode. In this embodiment, thecardioversion/defibrillation energy is delivered between the activesurface of the canister and the two coil electrodes 27 and 27′.Additionally, provided in the canister is means for selecting theoptimum sensing arrangement between the four sense electrodes 23, 23′,25, and 25′. The two electrodes are subcutaneously placed on the sameside of the heart. As illustrated in FIG. 6, one subcutaneous electrode13 is placed inferiorly and the other electrode 13′ is placedsuperiorly. It is also contemplated with this dual subcutaneouselectrode system that the canister and one subcutaneous electrode arethe same polarity and the other subcutaneous electrode is the oppositepolarity.

Turning now to FIGS. 12 and 13, further embodiments are illustratedwhere the canister 11 of the S-ICD of the present invention is shaped tobe particularly useful in placing subcutaneously adjacent and parallelto a rib of a patient. The canister is long, thin, and curved to conformto the shape of the patient's rib. In the embodiment illustrated in FIG.12, the canister has a diameter ranging from about 0.5 cm to about 2 cmwith about 1 cm being presently preferred. Alternatively, instead ofhaving a circular cross-sectional area, the canister could have arectangular or square cross-sectional area as illustrated in FIG. 13without falling outside of the scope of the present invention. Thelength of the canister can vary depending on the size of the patient'sthorax. Currently, the canister is about 5 cm to about 15 cm long withabout 10 cm being presently preferred. The canister is curved to conformto the curvature of the ribs of the thorax. The radius of the curvaturewill vary depending on the size of the patient, with smaller radiusesfor smaller patients and larger radiuses for larger patients. The radiusof the curvature can range from about 5 cm to about 25 cm depending onthe size of the patient. Additionally, the radius of the curvature neednot be uniform throughout the canister such that it can be shaped closerto the shape of the ribs. The canister has an active surface 15 that islocated on the interior (concave) portion of the curvature and aninactive surface 16 that is located on the exterior (convex) portion ofthe curvature. The leads of these embodiments, which are not illustratedexcept for the attachment port 19 and the proximal end of the lead 21,can be any of the leads previously described above, with the leadillustrated in FIG. 1 being presently preferred.

The circuitry of this canister is similar to the circuitry describedabove. Additionally, the canister can optionally have at least one senseelectrode located on either the active surface or the inactive surfaceand the circuitry within the canister can be programmable as describedabove to allow for the selection of the best sense electrodes. It ispresently preferred that the canister have two sense electrodes 26 and28 located on the inactive surface of the canisters as illustrated,where the electrodes are spaced from about 1 to about 10 cm apart with aspacing of about 3 cm being presently preferred. However, the senseelectrodes can be located on the active surface as described above.

It is envisioned that the embodiment of FIG. 12 will be subcutaneouslyimplanted adjacent and parallel to the left anterior 5th rib, eitherbetween the 4th and 5th ribs or between the 5th and 6th ribs. However,other locations can be used.

Another component of the S-ICD of the present invention is a cutaneoustest electrode system designed to simulate the subcutaneous high voltageshock electrode system as well as the QRS cardiac rhythm detectionsystem. This test electrode system is comprised of a cutaneous patchelectrode of similar surface area and impedance to that of the S-ICDcanister itself together with a cutaneous strip electrode comprising adefibrillation strip as well as two button electrodes for sending of theQRS. Several cutaneous strip electrodes are available to allow fortesting various bipole spacings to optimize signal detection comparableto the implantable system.

The S-ICD device and method of the present invention may be embodied inother specific forms without departing from the teachings or essentialcharacteristics of the invention. The described embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than by the foregoing description, and all changes whichcome within the meaning and range of equivalency of the claims are,therefore, to be embraced therein.

1. A method of implanting an implantable defibrillator in a patient, theimplantable defibrillator comprising a canister and a lead, the methodcomprising: making an incision in the left anterior axillary line;creating a subcutaneous pathway for implantation of the canistermedially of the incision and creating a canister location atapproximately the left inframammary crease; creating a subcutaneouspathway for implantation of the lead posteriorly from the incisiontoward the left posterior axillary line using a curved trocar;developing the subcutaneous pathway for implantation of the lead suchthat it terminates at a point that, if a straight line were drawn fromthe canister location to the termination point, the line would intersecta substantial portion of the left ventricular mass of the patient;inserting the lead into the subcutaneous pathway for implantation of thelead; and placing the canister medially of the incision at the canisterlocation.
 2. The method of claim 1 wherein the step of developing thesubcutaneous pathway for implantation of the lead comprises, aftercreating the subcutaneous pathway for implantation of the lead with thecurved trocar, inserting guidewire through the trocar; removing thecurved trocar and leaving the guidewire in place; inserting a stiffcurved peel away sheath over the guidewire; and removing the guidewire.3. The method of claim 2 wherein the step of inserting the lead isperformed by: inserting the lead into the stiff curved peel away sheathafter the guidewire is removed; and splitting and removing the stiffcurved peel away sheath.
 4. The method of claim 3 wherein the leadcomprises a distal end and a proximal end, the proximal end adapted forcoupling to the canister, wherein the distal end comprises an anchorsegment for anchoring into tissue such that the lead does not dislodgeafter implantation, wherein the method is performed such that the anchorsegment is emplaced to the termination point.
 5. The method of claim 4wherein the anchor segment comprises a tine.
 6. The method of claim 4wherein the anchor segment comprises a screw.
 7. The method of claim 4wherein the anchor segment comprises a hook.
 8. The method of claim 3wherein the lead comprises a distal end and a proximal end, the proximalend adapted for coupling to the canister, wherein the distal endcomprises a means for anchoring the lead into tissue such that the leaddoes not dislodge after implantation, wherein the method is performedsuch that the distal end is emplaced to the termination point.
 9. Themethod of claim 1 wherein the trocar includes a lumen and the methodfurther comprises injecting a fluid via the lumen during the step ofcreating a subcutaneous pathway for implantation of the lead.
 10. Themethod of claim 1 wherein the lead comprises a distal end and a proximalend, the proximal end adapted for coupling to the canister, wherein thedistal end comprises an anchor segment for anchoring into tissue suchthat the lead does not dislodge after implantation, wherein the methodis performed such that the anchor segment is emplaced to the terminationpoint.
 11. The method of claim 10 wherein the anchor segment comprises atine.
 12. The method of claim 10 wherein the anchor segment comprises ascrew.
 13. The method of claim 10 wherein the anchor segment comprises ahook.
 14. The method of claim 1 wherein the lead comprises a distal endand a proximal end, the proximal end adapted for coupling to thecanister, wherein the distal end comprises means for anchoring the leadinto tissue such that the lead does not dislodge after implantation,wherein the method is performed such that the distal end is emplaced tothe termination point.
 15. The method of claim 1 wherein the implantabledefibrillator further comprises a second lead and the method furthercomprises: creating a subcutaneous pathway for implantation of thesecond lead posteriorly from the incision to the left posterior axillaryline; and inserting the second lead into the subcutaneous pathway forimplantation of the second lead.
 16. The method of claim 15 furthercomprising: developing the subcutaneous pathway for implantation of thesecond lead such that it terminates at a point that, if a straight linewere drawn from the canister location to the termination point, the linewould intersect a substantial portion of the left ventricular mass ofthe patient.
 17. The method of claim 16 wherein each of the leadscomprise a distal end and a proximal end, the proximal end adapted forcoupling to the canister, wherein the distal end comprises an anchorsegment for anchoring into tissue such that the lead does not dislodgeafter implantation.
 18. The method of claim 16 wherein: each of theleads comprises a distal end and a proximal end, for each lead, theproximal end is adapted for coupling to the canister; and each leadcomprises means for anchoring the distal end of each respective leadinto tissue such that the lead does not dislodge after implantation. 19.A method of implanting an implantable defibrillator, the implantabledefibrillator comprising a canister and a lead, the method comprising:making an anterior incision on a patient's ribcage; creating a spaceadjacent the anterior incision near the left inframammary crease of thepatient for implantation of the canister; creating a subcutaneouspathway from the incision posteriorly to the left posterior axillaryline for implantation of the lead using at least a trocar and a peelaway sheath; leaving the peel away sheath in the subcutaneous pathwayfor implantation of the lead; implanting the lead through the peel awaysheath; removing the peel away sheath; and implanting the canister inthe space for implantation of the canister; wherein the lead has aproximal end adapted for coupling to the canister and a distal end, andthe lead comprises a means for anchoring the distal end of the lead tomaintain a posterior position of the lead.
 20. The method of claim 19wherein the step of creating a subcutaneous pathway for implantation ofthe lead comprises: inserting the trocar through the incision whileinjecting an anesthetic through a lumen of the trocar; inserting aguidewire through the trocar; removing the trocar; and advancing thepeel away sheath over the guidewire; wherein the peel away sheath is astiff curved peel away sheath; and wherein the step of leaving the peelaway sheath in the subcutaneous pathway for implantation of the leadcomprises removing the guidewire.